a 
ON THE ANATOMY OF THE ARANEIDEA, 161 
_ plainly seen in Agelena labyrinthica and Ciniflo ferox, but is still more distinct 
in some large foreign spiders. I have figured a sac and tube taken from a 
large species of Olios, which I had an opportunity of dissecting through the 
kindness of Dr. Gray of the British Museum (Plate XVII. fig.5). The ducts 
from these glands seem principally to terminate in the posterior and interme- 
diate spinnerets, but I have traced some of them (especially in Ciniflo ferox) 
into the anterior pair. When dissecting a large specimen of Mygale, I found 
that the fine ducts proceeding from the numerous small oval glands in the 
vicinity of the spinnerets had all the same structure as those I have described 
(Plate XVI. fig. 120). I have noticed that some of the larger ducts proceed 
parallel with, and are partly imbedded in, the fibres of the muscular bands 
which extend into the interior of the spinnerets (see Plate XVII. fig. 8). 
Ishall now endeavour to draw a few physiological inferences from the facts 
I have imperfectly related. Every papilla or spinning tube is furnished with 
a separate duct, so that each thread which a spider spins is secreted by a 
distinct gland having no communication with its neighbours; and there can 
be no doubt that different varieties of silk are secreted by the different kinds 
of glands; but it is exceedingly difficult to demonstrate the fact, as no direct 
experiments can well be made in proof of it. Treviranus says that he thinks 
the small glands near the spinnerets of Ciniflo atrox, the existence of which 
he ascertained (I do not mean the minute ones connected with the additional 
spinnerets), contain a different kind of fluid from that in the large sacs; but 
they are so small, that I do not think it possible to determine the nature of 
their contents except by the colour, and that must be influenced by the struc- 
ture of the walls of the sacs or glands. 
We have seen that the secreting glands are of very different sizes and kinds ; 
the orifices in the spinnerets, and the spinnerets themselves, are also different ; 
and reasoning upon these facts, and upon some points which may be con- 
sidered as proved, in the economy of the spinning organs, I think we may be 
justified in drawing certain conclusions, or rather offering suggestions as to 
their uses. 
I have said that in Cinzflo atrox and allied species there is a distinct pair 
of supplementary spinnerets, furnished with a fine sieve-like surface, for the 
emission of a number of exceedingly delicate threads; there are also a num- 
ber of very small and peculiar looking cells, apparently connected with these 
spinners; now Mr. Blackwall has distinctly shown that these spinnerets per- 
form a peculiar function, spinning exceedingly fine lines of pale blue silk, 
which is woven into a flocculus, as he calls it, by a most beautiful comb or 
calamistrum connected with the hind legs*, which flocculus performs a pecu- 
liar office in the webs of this spider. In this case there are a distinct set of 
glands, connected exclusively with a distinct pair of spinnerets, so that it is 
very easy to determine their functions; the other glands, however, have not 
peculiar spinnerets to themselves; therefore there must be a greater uncer- 
tainty in hazarding opinions as to their uses. 
By far the most numerous, and most constant in size and shape, of the 
spinning glands in spiders generally, are the small ones seated near the spin~ 
nerets; these probably secrete the finer threads which form the more deli- 
cate textures of their webs, construct the cocoons in which they enclose their 
eggs, and the retreats in which some of the species conceal themselves. 
I remarked that the hard cartilaginous sacs were peculiarly large and 
numerous in the geometric spiders, as Epéira diadema. I would suggest 
that they secrete the adhesive threads, which are spirally fixed upon the 
* Researches in Zoology, p. 273. 
